Hi Brendon
Welcome to IIS. You will find that others will chime in come the morning.
For your budget I'd stay away from 'conventional' scopes - eg refractors as well.
If you could stretch your budget a little further Andrews Communications in Sydney have the 8" Skywatcher Dobsonian for $599 ($150-$200 cheaper than elsewhere).
http://www.andrewscom.com.au/optical-telescopes
Many of us have bought gear from them and been happy with our purchases.
Alternatively you could consider a good pair of binoculars (not exactly my strong suit when it comes to advice).
With the current lockdown on social gatherings this next piece of advice isn't practical at the moment - but still worth considering before you make a purchase. And that is to get in touch with the folk at ASWA and try to attend one of their public events to talk with their members, look at and through their 'scopes - you may even find they have what you're after second hand.
https://aswa-inc.org.au/
If you check through the IIS classifieds you will find that there are currently two 8" Dobsonians for sale within your price range.
Most of the astronomers I know recommend that if you're getting a Dobsonian scope 8" is the best place to start.
Hopefully this info will take you a little farther along getting your 9 yer old son hooked into one of the most worthwhile hobbies going - astronomy!
All the best.
Paul